This invention relates to separating water and ions from solutions. More particularly, the invention relates to using polymer membranes or films for removing water from solutions or, stated in another way, for removing ions from water.
There are many processes involving the need for the removal of water from a process stream or the removal of contaminants from water streams before the water can be reused or released. Dewatering is of vital interest to the mining industry (e.g., lithium metal mining), the food industry (e.g., brines), the chemical industry (e.g., organics and ion removal), the pharmaceutical industry (e.g., product drying), the medical industry, and many environmental and waste remediation efforts. These separations can, in some cases, be accomplished by distillation. Distillation, however, is energy intensive and is often complicated by the presence of azeotropes. Polymer membranes have been recognized for years as an attractive alternative both energetically and economically. An energy efficient, chemically and thermally stable membrane could have a significant impact on all of these areas. Such a membrane could be used to deacidify water, to be a part of commercial and industrial deionizers, and to deionize distilled water to make ultrapure water for analytical chemistry uses. Unfortunately, the most common polymers used for routine water purification cannot survive the harsh conditions of industrial processes.
In recent years, the technology surrounding membranes and their use, for example in the separation of solutes from solution, has grown from simple laboratory procedures to industrial processes having considerable technical and commercial impact. Membranes are used on a large scale for many applications, among which are production of potable water from sea water by reverse osmosis, cleaning industrial effluents, recovering valuable constituents of solutions by electrolysis, and effecting various medical purposes.
In view of the foregoing, it will be appreciated that providing a method for economically and efficiently removing water or ions from solutions, especially from industrial solutions, would be a significant advancement in the art.
It is an object of the present invention to provide a method of economically and efficiently removing water or ions from solutions.
It is also an object of the invention to provide a method of using a chemically and thermally stable membrane for removing water or ions from solutions.
An illustrative method according to the present invention for separating ions from an aqueous stream containing such ions comprises:
(a) contacting a phosphazene polymer with the aqueous stream such that the ions are substantially prevented from permeating the phosphazene polymer, thereby producing an ion-depleted permeate stream and an ion-enhanced rejectate; and
(b) separately collecting the permeate stream and the rejectate.
In a preferred embodiment of the invention the phosphazene polymer is a member selected from the group consisting of linear polyphosphazenes, cyclo-linear polyphosphazenes, cyclo-matrix polyphosphazenes, and mixtures thereof. The phosphazene polymer also preferably comprises side-groups comprising organic functionality. For example, illustrative organic groups include phenoxy and octanoxy substituents.
Another preferred embodiment of the invention comprises a method for removing and concentrating ions from an aqueous ion-containing solution having a first volume comprising:
(a) contacting a phosphazene polymer with the ion-containing solution such that the ions are retained in an ion-enhanced rejectate and an ion-depleted permeate passes through the phosphazene polymer, wherein the ion-enhanced rejectate has a second volume, which is smaller than the first volume; and
(b) collecting the ion-enhanced rejectate.
Still another preferred embodiment of the invention comprises a method for dewatering an aqueous ion-containing solution stream comprising:
(a) contacting a phosphazene polymer with the aqueous stream such that the ions are substantially prevented from permeating the phosphazene polymer, thereby producing an ion-depleted permeate stream and an ion-enriched rejectate; and
(b) collecting the rejectate.